Passive accessory joint mobilizations are commonly used by rehabilitation clinicians to treat a variety of musculoskeletal pathologies, however, there is limited evidence regarding the mechanisms by which these treatments improve joint function. Joint mobilizations may improve joint function through both mechanical (positional) and functional (neuromuscular) mechanisms. We aim to assess the acute and intermediate positional and neuromuscular changes occurring at the ankle complex after a single bout of Maitland grade 3 anteroposterior (AP) mobilizations of the distal tibiofibular and talocrural joints in subjects with chronic lateral ankle instability (CLAI). The effects of mobilizations on the distal tibiofibular and talocrural joints will be examined independently in two separate randomized, controlled studies. CLAI provides an appropriate model to assess both the positional and neuromuscular effects of joint mobilizations because, compared to healthy controls, individuals with CLAI have been shown to have both positional faults at the distal tibiofibular (fibula displaced anteriorly relative to tibia) and talocrural (talus displaced anteriorly relative to tibia) joints, and impaired neuromuscular function about the ankle. To evaluate the effects of fibular mobilizations, 40 subjects with CLAI will have the following baseline measures taken: 1) relative AP position of the distal fibula in relation to the tibia as assessed on CT scans, 2) motoneuron pool excitability of the peroneus longus, soleus, and anterior tibialis as assessed with H-reflex testing, and 3) ankle dorsiflexion range of motion. Subjects will be randomly assigned to receive either the experimental treatment, a single session of AP distal fibular mobilizations, or the control treatment, a sham "laying of hands" procedure. Follow-up measures will be taken immediately after the respective treatment and one week later. To evaluate the effects of talar mobilizations, 40 subjects with CLAI will have the following baseline measures taken: 1) relative AP position of the talus in relation to the tibia as assessed on lateral radiographs, 2) motoneuron pool excitability of the peroneus longus, soleus, and anterior tibialis as assessed with H-reflex testing, 3) ankle dorsiflexion range of motion, and 4) talar displacement and stiffness during posterior translation of the rearfoot on the tibia as assessed with an ankle arthrometer. Subjects will be randomly assigned to receive either the experimental treatment, a single session of AP talar mobilizations, or the control treatment (same as previous study). Follow-up measures will be taken immediately after the respective treatment and one week later. For both studies, ANCOVAs will assess the effects of treatment (experimental, control) and time (baseline, immediate follow-up, 1 week) on the respective measures. Additionally, pre- post change scores from each measure at both follow-ups will be determined for the experimental group and bivariate correlation coefficients will be calculated to assess the direct relationships between the changes in the different measures after mobilization. The results of these randomized, controlled studies will elucidate the acute and intermediate mechanistic effects of joint mobilizations in regards to structural position and neuromuscular function at the ankle. PUBLIC HEALTH RELEVANCE: Passive accessory joint mobilizations are commonly used by rehabilitation clinicians to treat a variety of musculoskeletal pathologies, however, there is limited evidence regarding the mechanisms by which these treatments improve joint function. The results of these proposed studies will provide insight to the acute and intermediate mechanistic effects of joint mobilizations in regards to structural position and neuromuscular function at the ankle. This information will improve the understanding of the effects of joint mobilizations for both researchers and clinicians and potentially lead to advances in patient care for those suffering from musculoskeletal injuries.